Dr. Tomita uses LASIK Xtra, which combines a riboflavin ophthalmic solution with Avedro's KXL UVA irradiation system for CXL (pictured here) during LASIK Source: Minoru Tomita, M.D.
Corneal collagen crosslinking (CXL) is well known as an effective way to strengthen and stabilize the cornea in ectatic and keratoconic patients.
Minoru Tomita, M.D., executive director, Shinagawa LASIK Center, Tokyo, believes that using CXL as prophylaxis with LASIK is the obvious next use, especially considering that LASIK reportedly weakens the cornea anywhere from 20-40%.
Dr. Tomita uses LASIK Xtra
(Avedro, Waltham, Mass.), which combines a riboflavin ophthalmic solution (VibeX) with Avedro's KXL UVA irradiation system for CXL during LASIK. LASIK Xtra has CE mark approval but is not commercially available in the U.S. "Patients who choose LASIK Xtra are getting the benefits of
prevention of keratoectasia and
regression after LASIK," he said. "By performing crosslinking to regain the corneal conditions as closer to the strength at the pre-op stage, there is the potential to
prevent iatrogenic ectasia from
happening," Dr. Tomita continued. "Published papers have also reported the more corneal tissue ablated by LASIK, the thinner the cornea gets, which results in a higher likelihood of regression (myopic shift) due to the weakened cornea. When the cornea becomes strong after LASIK with crosslinking, it is likely to mitigate the occurrence and conditions of regression."
Dr. Tomita recommends the procedure for patients who are at risk for iatrogenic ectasia, such as high myopes who need a large amount of cornea ablated, patients with atopic dermatitis with less than 480 μm corneal thickness pre-op, or those who are at high risk for developing keratoconus or keratoectasia.
Never too thin?
Since CXL's primary purpose is to stiffen and stabilize, can it be deduced that adding the procedure to LASIK means surgeons will be able to operate on thinner corneas—ones they previously wouldn't have considered for the procedure? Despite positive outcomes in ectasia and keratoconus patients, Dan Z. Reinstein, M.D., medical director, London Vision Clinic, thinks that might be a bit of a leap.
"This implies, but does not prove, that we can do LASIK on thinner corneas if we also simultaneously crosslink, but it has to be proven," Dr. Reinstein said. "To date, there is no good method of measuring the biomechanical stiffening
effects of crosslinking; no machine seems to be able to pick up the changes with a parameter that we can actually measure. The area of
research is still young."
Dr. Reinstein said a 2010 study by Daniel Kampik, M.D., clinical research associate, and colleagues at University College London, Institute of Ophthalmology, showed that CXL does not change the LASIK ablation rate. "It does change nomograms, so this is a consideration if one wants to combine the two procedures," he said.
Risks and benefits
Avoiding ectasia is the primary benefit of combining CXL and LASIK, but a more predictable effect of LASIK has "yet to be proven," according to R. Doyle Stulting, M.D., Woolfson Eye Institute, Atlanta, and professor of ophthalmology, Emory University, Atlanta.
"Indications for the combination might include eyes at risk for ectasia, but some argue that PRK [photorefractive keratectomy] is a better procedure for those individuals," Dr. Stulting said. He added that he doesn't see a benefit to promoting routine CXL at the time of LASIK because of the downsides, including cost, risk of infection, additional
surgical time, and risk of endothelial cell damage. "Many would argue it is not a good idea for eyes at risk for ectasia because they would be better served by CXL and PRK," Dr. Stulting said. "They might also argue that it is not a good idea for eyes not at risk for ectasia."
Even the ectasia benefit remains to be seen, said retired Navy Capt. Steve C. Schallhorn, M.D., former director, Cornea Service & Refractive Surgery, Naval Medical Center, San Diego; and professor of ophthalmology, University of California, San Francisco.
"Because we do not know if CXL combined with primary LASIK will prevent ectasia, there is no way to assess the risk/benefit ratio," Dr. Schallhorn said. "No one has established evidence-based indications for the combination."
Dr. Schallhorn said he has yet to see clinical studies that combine primary LASIK with CXL.
"The issue is ectasia prevention, and ectasia can manifest years after LASIK," Dr. Schallhorn said. "Any studies would require long-term follow-up and need to be combined with a control population who underwent LASIK without CXL. This would be a difficult and expensive study to conduct."
Dr. Schallhorn doesn't believe it's a good idea to use CXL in primary LASIK procedures, especially if the patient is an otherwise excellent candidate for LASIK.
"In fact, promoting CXL with primary LASIK for all patients could do the community and the market great harm because essentially the message would be that LASIK without CXL is unsafe, which of course is not true."
Challenges would be additional surgical time and exposure to additional products (risk of infections), possible endothelial cell damage, and possible side effects of keratocyte death, Dr. Stulting said.
If the procedure isn't performed correctly, Dr. Tomita noted, complications could include severe DLK or increasing striae.
"When performed as instructed, the post-operative outcomes at 1 week are the same as the outcomes of regular LASIK performed without crosslinking," Dr. Tomita said. Dr. Tomita argued that using CXL as a preventative measure for eyes at risk of ectasia is better than post-op treatment because "treating iatrogenic ectasia is difficult once [it has] developed."
Dr. Reinstein echoed Dr.
Schallhorn's sentiment about safety benefits needing to be proven over a long time period. Meanwhile, LASIK remains a safe procedure, and if performed properly, ectasia development may not be as big a risk as some think. "In any case, there is no need for crosslinking in LASIK if current safety criteria with respect to corneal thickness and residual stromal thickness are observed," he said. "There have been over 20 million procedures performed to date, and the long-term safety with respect to ectasia is excellent, particularly with the use of thin flaps created by femtosecond lasers. It is hard to justify crosslinking in routine cases at this point."
Editors' note: Dr. Schallhorn has
financial interests with Abbott Medical Optics (Santa Ana, Calif.). Dr. Tomita has financial interests with Avedro. Drs. Reinstein and Stulting have no
financial interests related to this
Reinstein: +44 020 7224 1005,
Schallhorn: 619-920-9031, firstname.lastname@example.org
Tomita: +81-3-5221-2207, email@example.com